This invention relates to a device for controlling automatically the ignition timing of an internal combustion engine in such a way as to reduce or eliminate "pre-ignition" or so-called "knocking". Such anti-knock devices will be referred to for convenience in this specification and in the attached claims as "knocking controls".
Devices for controlling ignition timing of an engine are known, in which the ignition timing is stored within maps, depending upon various parameters such engine speed in particular, and is adjusted according to the instantaneous running condition of the engine. These programmed ignition timing angles are "advanced" as far as possible in relation to the top dead center position of the engine in order to obtain effective running with high power, low fuel consumption and low emission of toxic substances. As a result, the "knocking limit" is nearly reached, with consequent danger of knocking combustion; i.e. pre-ignition and possible damage to the engine.
In order to be able to achieve effective operation close to the "knocking limit" but avoid damage to the engine, it is also known to incorporate a so-called knocking control in addition to the aforementioned map adjustment of the ignition timing. Such a knocking control means essentially comprises a knocking sensor for determining pressures or noises, an evaluating circuit connected thereto, a signal processing means for recognizing and distinguishing knocks as compared with other noises, and also a control circuit. The control circuit adjusts the spark advance by steps in the retarding direction, when knocks are detected. An adjustment of the ignition point away from the knocking limit consequently occurs with the aid of this knocking control, when knocks are detected. When knocks no longer occur, re-regulation or resetting of the ignition point occurs again in steps in the advancing direction, towards the knocking limit. The stepwise control provides that for each detected knock a certain retarding adjustment of the ignition point occurs and this is sustained for a certain programmed number of combustions or engine cycles. If a further knock occurs, a further retarding adjustment takes place, and if there is no further knock, re-regulation or an advancing step occurs again to shift the ignition point back towards the knocking limit, until a knock is once again detected or the pre-programmed value in the map is obtained.
The control system described above continues to operate in the same way when engine acceleration occurs. As is well-known knocking frequently occurs during acceleration and with load variations which are associated therewith, and these are sensed by the knocking control means and can lead to considerable retarding adjustments of the ignition point. The result of this, however, is that the engine is operated less effectively, with lower power, higher fuel consumption and higher emissions of toxic substances. However, particularly under acceleration conditions, it is disadvantageous if the potential engine power is reduced by retarding the ignition point, as the active security of the vehicle in traffic is reduced.